1. Field of the Invention
The present invention relates to a physical quantity conversion sensor and a motor control system using the physical quantity conversion sensor. More particularly, the invention relates to a physical quantity conversion sensor well suited for using magneto-resistance effect elements as sensors, and a motor control system using the physical quantity conversion sensor.
2. Description of the Related Art
In a servo control system, rotation angle sensors are necessary to implement feedback control by detecting the rotation angle. In addition, in brushless motor control, rotation angle sensors are necessary not only for the servo control system but also for others because the current has to be applied to coils of a motor in correspondence to the rotation angle of the motor.
Further, a high level of safety is required in the case the system using the rotation angle sensors are applied to, for example, x-by-Wire that controls the behavior of the automobile vehicle body through integral control of electric power steering, electric braking, and electrically-controlled throttle devices, a steering system, and a braking system. Conventionally, a redundant technique preliminarily including an excessive number of components has been widely employed to satisfy the requirement for such a high level of safety, that is, to detect abnormality.
The rotation angle sensor using magnetism includes sensor elements that output signals proportional to the sine (“sin”) and cosign (“cos”) of the rotation angle, and conversion processing sections that obtain the rotation angle from the signals proportional to the sine (“sin”) and cosign (“cos”) from the sensor elements. According to conventional technique, however, the components are mounted in discrete packages, or as described in Non-patent Publication 1 below (*), the components are all mounted in a single package.    (*) Non-patent Publication: “KMA200, Programmable angle sensor,” Rev.05-16 Aug. 2005, Product data sheet, Koninklijke Philips Electronics N.V. 2005)
As described in Non-patent Publication 1, the technique in which the sensor elements and conversion processing section are mounted in the single package is effective in cost reduction associated with reduction in size and the number of connections, and in reliability improvement. However, it is desired to further take extensibility in regard to “non-redundant configuration→redundant configuration” into consideration.
For application to a use case that requires a high reliability such as described above, redundancy is necessary for the conversion processing section to implement fault detection. On the other hand, however, in many cases, since the sensor elements output two signals proportional to the sine (“sin”) and cosign (“cos”) of the rotation angle, the sensor elements already have redundancy in a certain extent; that is, further redundancy is not necessary. For example, when the characteristic represented by “(sin θ)2+(cos θ)2=1” is utilized, whether a determination can be made whether the output of the respective sensor element is normal or abnormal. However, in the technique in which the sensor elements and the conversion processing section are mounted in the single package, two packages have to be preliminarily provided, as described in Non-patent Publication 1. That is, excessive redundancy has to be provided for the convenience of the mounting or implementation method. This leads to cost elevation.